The present invention relates to a developer dispensing apparatus for a developer station in a xerographic printing machine and, more particularly, to an apparatus which utilizes a helical spring as an auger mechanism. In prior art printing machines, the toner material used to develop a latent image formed on a photoreceptor surface is consumed in a development process and must be periodically replaced within the development system in order to sustain continuous operation of the machine. One technique which has become generally accepted is the use of a separate toner or developer hopper with a dispensing mechanism for adding the toner from the hopper to the developer apparatus on a regular, or as needed, basis. In addition, it has become common practice to provide replenishing toner supplies in a sealed container which, when placed in the automatic printing machine, can be automatically opened to dispense toner. In such systems a difficulty may arise in uniformly dispensing the developer since, in a large mass of toner particles, which frequently is somewhat tacky, the particles may tend to agglomerate, become compacted and form a bridging structure in the toner container.
Various devices have been used to overcome the above-noted problems. For example, in the xerox 1025 Copier, the toner hopper is provided with a coiled spring auger which moves the toner material from one end of the hopper to the other. In this type of system, the auger is driven about one end and unsupported at the other end. Difficulties may be experienced in two areas. Depending upon the developer composition, the free end of the coiled spring auger may ride upward through the developer bed. By failing to stay completely submerged within the developer bed, the transport efficiency is reduced. In addition, for a system in which a toner bottle has an auger to transport toner therein which is driven and supported about one end and intended to dispense toner through a dispensing opening at the other end, as the auger is rotatably driven tending to drive toner toward the dispensing end the amount of toner at the dispensing end increases and tends to become compacted forming a bridge which tends to provide a force on the spring auger compressing it in a direction toward the driven end. If this force becomes too great, it may force the auger spring end past the dispensing opening in the toner cartridge thereby removing the antibridging function of the auger at the dispensing opening resulting in bridging over the dispensing opening and a lack of flow of toner out of the toner cartridge.
Anti-bridging devices utilizing wire spring augers are known in the art. For example, U.S. Pat. No. 4,739,907 issued on April 26, 1988 and assigned to the same assignee as the present invention, and U.S. Pat. No. 3,724,725 issued April 3, 1973 and assigned to IBM, disclose two spring members located within a toner dispenser which are rotated past each other in opposing directions. However, these disclosures do not consider the problem of unwanted movement of the spring auger at the free end.
The present invention is therefore directed to a developer dispensing apparatus which utilizes a helical spring auger to dispense toner within a toner housing. Means are provided to interact with the free end of the spring to both restrain an upward motion of the free end of the spring as well as to impart an anti-bridging effect to the toner transport. More particularly, the invention is directed towards a developer dispensing appartus including an elongated container enclosed at both ends having a substantially circular cross section capable of containing a given quantity of developer, said container having a dispensing opening adjacent one end and containing an integral developer transport mixing member rotatably supported at the opposite end of said container and unsupported at said one end, said mixing member comprising a coiled spring element adapted to rotate in a direction so as to transport developer along its length toward said dispensing opening, said dispensing apparatus characterized by a mixing member hold down element fixedly attached to the container end associated with the unsupported end of said spring element, at least a portion of said spring element rotatably encircling said hold down element, whereby any vertical movement of the unsupported end of said mixing member during rotation is restrained by the mechanical contact with the adjacent surface of said hold down element.